Heat the oil in a large pan. Sizzle the
pancetta for about 3 mins on each side
until crisp, then remove to a plate and
set aside. Melt the butter in the same
pan, add the onion, bay leaf and thyme
stalks, and cook for 10 mins until just
starting to turn golden. Add the celeriac
and cook for 2 mins more.
Pour over the stock and simmer
for 10 mins until the celeriac is soft.
Stir in the cream and bring back to
the boil. Fish out the bay and thyme
stalks, then purée the soup until
smooth. Stir through half the thyme
leaves and ladle the soup into bowls.
Serve topped with the crispy pancetta,
the remaining thyme leaves and a
drizzle of olive oil.